24‭ March 1968: The Aer Lingus plane, St Phelim, plunged into the Irish Sea off the Tuskar Rock on this day. Just after noon on a fine spring day the aircraft inexplicably plunged into the Irish Sea off the County Wexford coast from a height of 17,000 ft, killing all 61 passengers and crew on board.

Flight 712 had taken off from Cork airport about 30 minutes beforehand and was due to land at Heathrow, London. The plane was a propeller driven Vickers Viscount 803 with no known structural defects that could explain the sudden loss of this aircraft. ‬Of the 57 passengers, 35 were Irish, nine were Swiss, six were from Belgium, five were British, and two were American.  Of the 61 people on board only 14 bodies were ever recovered.

Its penultimate,‭ garbled message indicated another aircraft was in the area. In its last message, eight seconds later, co-pilot Paul Heffernan, aged 22, said: "12,000 ft descending, spinning rapidly.":

‭Witnesses say Captain Barney O'Beirne,‭ aged 35, managed to level the four-engine plane about 1,000 ft above the water, and flew on for about 15 minutes before it crashed close to Tuskar Rock. There was no black box recorder on the aircraft, which had undergone a major inspection three weeks earlier.

The Guardian‭ 11 January 1999

Speculation over the years has centred around the possibility that the plane was shot down by a rogue British test missile fired from an RAF base in Wales.‭ Still to this day, there are no definite answers as to what happened. The AAIU investigation reported that a structural failure of the port tailplane metal fatigue, corrosion, flutter (vibration in a control surface which may cause control difficulty and lead to a structural failure) or a bird strike may have been the cause. However no set of established facts has ever been able to show what actually caused the plane to crash with such a devastating loss of life.

The St Phelim Disaster is the worst ever recorded in the history of Irish Aviation.